A typical automobile hood inner panel often has such a structure that its outer peripheral portion is joined by folding an hood outer panel (hem working) and it has therein an outer peripheral skeleton portion disposed at the outer peripheral portion and having a substantially annular shape, the skeleton portion having an recessed-top cross sectional shape orthogonal to the circumferential direction of the annular shape, and an outer proximal surface extending inwardly from the outer peripheral skeleton portion and mastic-joined with the hood outer panel. A hinge and a striker are joined to the bottom surface of such an outer peripheral skeleton portion, and a cushion rubber seating surface or the like is formed on the bottom surface of such an outer peripheral skeleton portion, and the bottom surface of such an outer peripheral skeleton portion is connected to or supported by an automobile body under the hood with these therebetween.
The outer peripheral skeleton portion of the hood inner panel forms, together with the hood outer panel, a substantially annular frame structure on the outer periphery of the hood panel, thereby ensuring the rigidity as a hood. In order to increase this rigidity, it is required to deepen and widen the recessed shape of the outer peripheral skeleton portion without interfering with other parts, and without influencing the collision performance such as pedestrian protection or frontal collision performance, or panel rigidity, dent resistance, and the like.
On the other hand, the outer proximal surface extending inwardly from the outer peripheral skeleton portion and mastic-joined with the hood outer panel is provided for the purpose of ensuring the panel rigidity and dent resistance of the hood. In order to ensure these performances in a wide range, it is desired to set the position of mastic-joining with the hood outer panel as close as possible to the outer peripheral portion. For this reason, in order to achieve both hood rigidity and panel rigidity or dent resistance, the angle of a vertical wall connecting the outer proximal surface and the bottom surface of the outer peripheral skeleton portion is often set relatively steep.
However, it is problematic that the steeper the angle of the vertical wall, the less likely the vertical wall is to deform during a pedestrian head collision. Since, as described above, the outer peripheral portion of the hood is connected to or supported by the body of the automobile with a hinge, a striker, cushion rubber, or the like therebetween, the hood itself is less likely to move downward. For this reason, collision energy needs to be absorbed efficiently at a short distance between the bottom surface of the outer peripheral skeleton portion that is connected to the body of the automobile and the hood outer panel. If, in this case, the deformation of the hood inner panel such as the vertical wall described above is less likely to occur, the hood inner panel does not sufficiently deform during pedestrian head collision, a secondary peak is generated in the acceleration during the collision, and the head injury criteria (HIC) value worsens.
To solve such a problem, some approaches are proposed in which, in the vertical wall on the front, side of the hood, a shelf portion triggering deformation is provided in the middle of the vertical wall, and the deformation during a pedestrian head collision is thereby promoted to ensure the pedestrian protection performance (see, for example, PTLs 1 and 2).
Some cases are proposed in which, in order to reduce the HIC value during a pedestrian head collision, a weakening portion such as a folding line or a slit is set in the vertical wall although these cases are intended for a lock reinforcing material or dent reinforcing material disposed on the front side of the hood (see, for example, PTLs 3 and 4).
A structure is proposed in which a trim hole including the bottom surface of the outer peripheral skeleton portion is set in the vicinity of a corner part of the vertical wall (see, for example, PTL 5).
Some structures are proposed in which for the purpose of providing a weakening portion in part of the hood inner panel to improve the collision performance such as pedestrian protection performance, a trim hole is set in the vicinity of a bead setting part in the center of the hood inner panel (see, for example, PTLs 6 to 14).